WPF TextBox 不能输入，求大大帮忙！

在WPF中写了个TextBox，样式用的是别人的。可是输入框不能输入了。
求大虾帮忙看看是什么问题导致的，怎么解决！
<Window x:Class="Test.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <Style x:Key="LoginTextBoxStyle" TargetType="TextBox">
            <Setter Property="BorderThickness" Value="1"/>
            <Setter Property="Background" Value="#FFFFFFFF"/>
            <Setter Property="Foreground" Value="#FF000000"/>
            <Setter Property="Padding" Value="2"/>
            <Setter Property="BorderBrush">
                <Setter.Value>
                    <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                        <GradientStop Color="#FFA3AEB9" Offset="0"/>
                        <GradientStop Color="#FF8399A9" Offset="0.375"/>
                        <GradientStop Color="#FF718597" Offset="0.375"/>
                        <GradientStop Color="#FF617584" Offset="1"/>
                    </LinearGradientBrush>
                </Setter.Value>
            </Setter>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="TextBox">
                        <Grid x:Name="RootElement">
                            <VisualStateManager.VisualStateGroups>
                                <VisualStateGroup x:Name="FocusStates">
                                    <VisualState x:Name="Focused">
                                        <Storyboard>
                                            <ColorAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="rectangle" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[0].(GradientStop.Color)">
                                                <SplineColorKeyFrame KeyTime="00:00:00.1000000" Value="#FFCBFB82"/>
                                            </ColorAnimationUsingKeyFrames>
                                            <ColorAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="rectangle" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)">
                                                <SplineColorKeyFrame KeyTime="00:00:00.1000000" Value="#FFCFFE54"/>
                                            </ColorAnimationUsingKeyFrames>
                                            <ColorAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="rectangle1" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[0].(GradientStop.Color)">
                                                <SplineColorKeyFrame KeyTime="00:00:00.1000000" Value="#FF94E650"/>
                                            </ColorAnimationUsingKeyFrames>
                                            <ColorAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="rectangle1" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)">
                                                <SplineColorKeyFrame KeyTime="00:00:00.1000000" Value="#FFCFFE54"/>
                                            </ColorAnimationUsingKeyFrames>
                                        </Storyboard>
                                    </VisualState>
                                    <VisualState x:Name="Unfocused">
                                        <Storyboard>
                                            <ColorAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="rectangle" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[0].(GradientStop.Color)">
                                                <SplineColorKeyFrame KeyTime="00:00:00.1000000" Value="#FFF9F9F9"/>
                                            </ColorAnimationUsingKeyFrames>
                                            <ColorAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="rectangle" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)">
                                                <SplineColorKeyFrame KeyTime="00:00:00.1000000" Value="#FFFEFEFE"/>
                                            </ColorAnimationUsingKeyFrames>
                                            <ColorAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="rectangle1" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[0].(GradientStop.Color)">
                                                <SplineColorKeyFrame KeyTime="00:00:00.1000000" Value="#FFE7E7E7"/>
                                            </ColorAnimationUsingKeyFrames>
                                            <ColorAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="rectangle1" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)">
                                                <SplineColorKeyFrame KeyTime="00:00:00.1000000" Value="#FFFEFEFE"/>
                                            </ColorAnimationUsingKeyFrames>
                                        </Storyboard>
                                    </VisualState>
                                </VisualStateGroup>
                            </VisualStateManager.VisualStateGroups>
                            <Border x:Name="Border" Opacity="1" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="1">
                                <Grid>
                                    <Grid HorizontalAlignment="Stretch" Width="Auto">
                                        <Rectangle Margin="0,0,0,0" Stroke="{x:Null}" RadiusX="20.333" RadiusY="20.333" x:Name="rectangle">
                                            <Rectangle.Fill>
                                                <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                                                    <GradientStop Color="#FFF9F9F9"/>
                                                    <GradientStop Color="#FFFEFEFE" Offset="1"/>
                                                </LinearGradientBrush>
                                            </Rectangle.Fill>
                                        </Rectangle>
                                        <Rectangle Margin="0,3,0,0" Stroke="{x:Null}" RadiusX="20.333" RadiusY="20.333" x:Name="rectangle1">
                                            <Rectangle.Fill>
                                                <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                                                    <GradientStop Color="#FFE7E7E7"/>
                                                    <GradientStop Color="#FFFEFEFE" Offset="1"/>
                                                </LinearGradientBrush>
                                            </Rectangle.Fill>
                                        </Rectangle>
                                    </Grid>
                                    <Border x:Name="ReadOnlyVisualElement" Opacity="0" Background="#72F7F7F7"/>
                                    <Border x:Name="MouseOverBorder" BorderBrush="Transparent" BorderThickness="1">
                                        <ScrollViewer x:Name="ContentElement" BorderThickness="0" IsTabStop="False" Padding="{TemplateBinding Padding}" Margin="89,0,17,0" VerticalAlignment="Center" VerticalContentAlignment="Stretch"/>
                                    </Border>
                                </Grid>
                            </Border>
                            <Border x:Name="DisabledVisualElement" IsHitTestVisible="False" Opacity="0" Background="#A5F7F7F7" BorderBrush="#A5F7F7F7" BorderThickness="{TemplateBinding BorderThickness}"/>
                            <Border Margin="1" x:Name="FocusVisualElement" IsHitTestVisible="False" Opacity="0" BorderBrush="#FF6DBDD1" BorderThickness="{TemplateBinding BorderThickness}"/>
                        </Grid>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>
    <Grid Height="54" HorizontalAlignment="Left" Margin="20,111,0,0" x:Name="AccountGrid" VerticalAlignment="Top" Width="426">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="73"/>
            <ColumnDefinition Width="1"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <TextBox x:Name="tbUserAccount" HorizontalAlignment="Stretch" Margin="0,0,0,0" Style="{StaticResource LoginTextBoxStyle}" VerticalAlignment="Stretch" Background="{x:Null}" BorderBrush="{x:Null}" FontFamily="Verdana" FontSize="24" FontWeight="Bold" Foreground="#FF393B3D" Grid.Column="0"  Text="" TextWrapping="NoWrap" Grid.ColumnSpan="3" Padding="0,0,0,0">
        </TextBox>
        <TextBlock IsHitTestVisible="False" HorizontalAlignment="Right" Margin="0,15,12,0" VerticalAlignment="Top" FontFamily="Microsoft YaHei" FontSize="16" Foreground="#FF9B9B9B" Text="帐号" TextWrapping="Wrap"/>
        <Rectangle IsHitTestVisible="False" Margin="0,6,0,3" Opacity="0.3" Grid.Column="1" Grid.ColumnSpan="1" Fill="#FFC7C7C7" Stroke="{x:Null}"/>
    </Grid>
</Window>WPFtextbox